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In the Geodetic Set problem, the input consists of a graph G and a positive integer k. The goal is to determine whether there exists a subset S of vertices of size k such that every vertex in the graph is included in a shortest path between two vertices in S. Kellerhals and Koana [IPEC 2020; J. Graph Algorithms Appl 2022] proved that the problem is W[1]-hard when parameterized by the pathwidth or the feedback vertex set number of the input graph. They posed the question of whether the problem admits an XP-algorithm when parameterized by the combination of these two parameters. We answer this in the negative by proving that the problem remains NP-hard even on graphs of constant pathwidth and feedback vertex set number.
@InProceedings{tale:LIPIcs.IPEC.2025.28,
author = {Tale, Prafullkumar},
title = {{Geodetic Set on Graphs of Constant Pathwidth and Feedback Vertex Set Number}},
booktitle = {20th International Symposium on Parameterized and Exact Computation (IPEC 2025)},
pages = {28:1--28:14},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-407-9},
ISSN = {1868-8969},
year = {2025},
volume = {358},
editor = {Agrawal, Akanksha and van Leeuwen, Erik Jan},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2025.28},
URN = {urn:nbn:de:0030-drops-251601},
doi = {10.4230/LIPIcs.IPEC.2025.28},
annote = {Keywords: Geodetic Sets, NP-hardness, Constant Treewidth}
}